diff --git a/packages/das/src/api/miners/pagination.spec.ts b/packages/das/src/api/miners/pagination.spec.ts
new file mode 100644
index 0000000..69caff9
--- /dev/null
+++ b/packages/das/src/api/miners/pagination.spec.ts
@@ -0,0 +1,111 @@
+import { BadRequestException } from "@nestjs/common";
+import { decodeCursor, encodeCursor, parsePaginationQuery } from "./pagination";
+
+// Decoded cursor fields are bound to `::timestamptz` / `::int` casts in the
+// keyset WHERE clause. decodeCursor must reject any payload Postgres would
+// choke on — a tampered or truncated cursor has to come back as a 400, not
+// bubble up as a QueryFailedError 500.
+
+function rawCursor(payload: Record<string, unknown>): string {
+  return Buffer.from(JSON.stringify(payload), "utf8").toString("base64url");
+}
+
+describe("decodeCursor", () => {
+  it("round-trips a cursor produced by encodeCursor", () => {
+    const encoded = encodeCursor({
+      created_at: new Date("2026-06-01T12:34:56.000Z"),
+      repo_full_name: "Entrius/Das-GitHub-Mirror",
+      pr_number: 42,
+    });
+
+    expect(decodeCursor(encoded)).toEqual({
+      createdAt: "2026-06-01T12:34:56.000Z",
+      repoFullName: "entrius/das-github-mirror",
+      number: 42,
+    });
+  });
+
+  it("rejects a cursor that is not base64url JSON", () => {
+    expect(() => decodeCursor("not-a-cursor")).toThrow(BadRequestException);
+  });
+
+  it("rejects a cursor whose created_at is not a parseable timestamp", () => {
+    const encoded = rawCursor({
+      created_at: "banana",
+      repo_full_name: "acme/repo",
+      number: 1,
+    });
+
+    expect(() => decodeCursor(encoded)).toThrow(BadRequestException);
+  });
+
+  it("rejects a cursor whose number is not an integer", () => {
+    const encoded = rawCursor({
+      created_at: "2026-06-01T00:00:00.000Z",
+      repo_full_name: "acme/repo",
+      number: 1.5,
+    });
+
+    expect(() => decodeCursor(encoded)).toThrow(BadRequestException);
+  });
+
+  it("rejects a cursor with missing or mistyped fields", () => {
+    expect(() =>
+      decodeCursor(rawCursor({ repo_full_name: "acme/repo", number: 1 })),
+    ).toThrow(BadRequestException);
+    expect(() =>
+      decodeCursor(
+        rawCursor({
+          created_at: "2026-06-01T00:00:00.000Z",
+          repo_full_name: 7,
+          number: 1,
+        }),
+      ),
+    ).toThrow(BadRequestException);
+    expect(() =>
+      decodeCursor(
+        rawCursor({
+          created_at: "2026-06-01T00:00:00.000Z",
+          repo_full_name: "acme/repo",
+          number: "1",
+        }),
+      ),
+    ).toThrow(BadRequestException);
+  });
+});
+
+describe("parsePaginationQuery", () => {
+  it("propagates cursor validation instead of passing garbage to SQL", () => {
+    const encoded = rawCursor({
+      created_at: "not-a-date",
+      repo_full_name: "acme/repo",
+      number: 1,
+    });
+
+    expect(() => parsePaginationQuery("50", encoded)).toThrow(
+      BadRequestException,
+    );
+  });
+
+  it("returns null when neither limit nor cursor is provided", () => {
+    expect(parsePaginationQuery(undefined, undefined)).toBeNull();
+    expect(parsePaginationQuery("", "")).toBeNull();
+  });
+
+  it("accepts a valid limit with a valid cursor", () => {
+    const encoded = encodeCursor({
+      created_at: "2026-06-01T00:00:00.000Z",
+      repo_full_name: "acme/repo",
+      issue_number: 7,
+    });
+
+    expect(parsePaginationQuery("25", encoded)).toEqual({
+      limit: 25,
+      cursor: {
+        createdAt: "2026-06-01T00:00:00.000Z",
+        repoFullName: "acme/repo",
+        number: 7,
+      },
+    });
+  });
+});
diff --git a/packages/das/src/api/miners/pagination.ts b/packages/das/src/api/miners/pagination.ts
index c39e44d..bce062a 100644
--- a/packages/das/src/api/miners/pagination.ts
+++ b/packages/das/src/api/miners/pagination.ts
@@ -61,11 +61,18 @@ export function decodeCursor(raw: string): DecodedCursor {
     throw new BadRequestException("cursor is invalid");
   }
 
+  // The decoded fields feed `::timestamptz` / `::int` casts in the keyset
+  // WHERE clause, so anything Postgres would reject must be caught here —
+  // otherwise a tampered/truncated cursor surfaces as a QueryFailedError
+  // 500 instead of a 400. encodeCursor only ever emits toISOString()
+  // timestamps and integer PR/issue numbers, so no legitimate cursor is
+  // rejected by these checks.
   if (
     typeof payload.created_at !== "string" ||
+    Number.isNaN(Date.parse(payload.created_at)) ||
     typeof payload.repo_full_name !== "string" ||
     typeof payload.number !== "number" ||
-    !Number.isFinite(payload.number)
+    !Number.isInteger(payload.number)
   ) {
     throw new BadRequestException("cursor is malformed");
   }